1. Field of the Invention
The present invention relates to a compound consisting of a glycosaminoglycan conjugated with a drug and to a preparation method thereof as well.
2. Description of the Prior Arts
The extracellular matrix (ECM) is a dynamic assemblage of interacting molecules that regulate cell functions and interactions in response to stimulation. One class of extracellular matrix macromolecules, the glycosaminoglycans, are molecules known to be involved in a wide array of both normal and abnormal biological processes, including cell migration, differentiation, proliferation, immune response and cytoskeletal organization.
Glycosaminoglycans (GAGs) are unbranched chains composed of repeating disaccharide units. These disaccharide units always contain an amino sugar (N-acetylglucosamine or N-acetylgalactosamine), which in most cases is sulfated, with the second sugar usually being an uronic acid (glucuronic or iduronic). GAGs are highly negatively charged because of the presence of carboxyl or sulfate groups on most of their sugar residues. As such they are strongly hydrophilic. GAGs tend to adopt highly extended conformations and form matrices that are space filling and resistant to compressive forces. Four main groups of GAGs have been distinguished by their sugar residues, the type of linkage between these residues, and the number and location of sulfate groups. They include: (1) hyaluronan, (2) chondroitin sulphate and dermatan sulfate, (3) heparan sulfate and heparin, and (4) keratan sulfate.
Hyaluronan (also called hyaluronic acid or hyaluronate or HA) is the simplest of GAGs. It consists of a regular repeating sequence of non-sulfated disaccharide units, specifically N-acetylglucosamine and glucuronic acid. Its molecular weight can range from 400 daltons (the disaccharide) to over millions of daltons. It is found in variable amounts in all tissues, such as the skin, cartilage, and eye, and in most, if not all, fluids in adult animals. It is especially abundant in early embryos. In articular cartilage, HA can form a large aggregate which is important for the function of cartilage. Furthermore, cell motility and immune cell adhesion is mediated by the cell surface receptor RHAMM (Receptor for Hyaluronan-Mediated Motility) and CD44.
HA is synthesized directly at the inner membrane of the cell surface with the growing polymer extruded through the membrane to the outside of the cell as it is being synthesized. Synthesis is mediated by a single protein enzyme, hyaluronan synthetase (HAS). By contrast, other GAGs are synthesized inside the cell in the Golgi apparatus, possibly in association with some core protein, and then released by exocytosis. HA degradation in vertebrate tissues in vivo is mediated by hyaluronidase, and exoglycosidases that remove sugars sequentially. Mammalian-type hyaluronidases have both hydrolytic and transglycosidase activities and can degrade HA and chondroitin. In connective tissue, the water of hydration associated with HA creates spaces between tissues, thus creating an environment conducive to cell movement and proliferation. HA plays a key role in biological phenomena associated with cell motility including rapid development, regeneration, repair, embryogenesis, embryological development, wound healing, angiogenesis, and tumorigenesis.
CD44 (also known as Pgp-1, Hermes-3, HCAM, ECMR III) is a widely expressed glycoprotein with a molecular weight of 85 to 90 kDa. CD44 is a major cell surface receptor for the glycosaminoglycan, hyaluronic acid (HA). CD44 binds HA specifically, although certain chondroitin-sulfate containing proteoglycans may also be recognized. CD44 plays a role in various cellular and physiological functions, including adhesion to and migration on HA, HA degradation and tumor metastasis. CD44 has also been shown to play a role in extracellular matrix binding, cell migration, lymphocyte activation, lymphocyte homing, and proliferation of bronchial smooth muscle cell (Gunthert et al., 1991, A new variant of glycoprotein CD44 confers metastatic potential to rat carcinoma cells, 5;65(1):13-24). The CD44 receptor shows a complex pattern of alternative splicing in its variable region of the extracellular domain. CD44 appears to be a particularly important leukocyte receptor for HA and may therefore have a role in the pathogenesis of asthma. In addition, levels of HA, which were increased during experimental asthma in control mice were markedly attenuated in the antibody-treated mice, supporting a role for CD44 in HA metabolism (specifically in the breakdown of high molecular weight HA to pro-inflammatory low molecular weight forms). This may be particularly important because HA-derived oligosaccharides can bind and activate Toll-like receptor. Clearly, the most impressive aspect of the results is the profound magnitude of the beneficial effects of anti-CD44 treatment.
HA-CD44 interactions may play an important role in development, inflammation, T cell recruitment and activation, lung inflammation, and tumor growth and metastasis. Altered expression of alternatively spliced CD44 transcripts has been found in many cancers, including cancer of the stomach (F Reihani-S abet et al., 2003, Effects of Inflammation and H. pylori Infection on Expression of CD44 Variant Exons in Gastric Tissue, Journal of Sciences, 14:11-16).
Malignant tumor cells could selectively ingest proportionally more of bioconjugates than normal connective tissue or mesenchymal cells due to their overexpression of the CD44 receptor. Several studies have correlated increased HA synthesis and uptake with cancer progression and metastatic potential. Certain tumors, including many that are found in the lung, overexpress the CD44 cell-surface marker. Breast cancer cells are known to have greater uptake of HA than normal tissues, requiring HA for high P-glycoprotein expression, the primary contributor to multi-drug resistance. Furthermore, invasive breast cancer cells overexpress CD44, the primary receptor for HA, and are dependent on high concentrations of CD44-internalized HA for proliferation. Thus, chemotherapeutic drug nanoconjugates with HA may be efficacious against lymphatic metastases. (Eliaz, R. E. et al., 2004, Liposome-encapsulated doxorubicin targeted to CD44: a strategy to kill CD44-overexpressing tumor cells, Cancer Res., 61(6):2592-601).
Non-steroidal anti-inflammatory drugs (NSAIDs) and selective inhibitors of cyclooxygenase (COX)-2, are therapeutic groups generally used for the treatment of pain, inflammation and fever. Recently, growing experimental implies that some NSAIDs and the selective COX-2 inhibitors may also have anti-cancer activity by involving in multiple biologic events throughout the tumorigenic process. For example, epidemiological studies have shown that regular use of Aspirin reduces the risk of developing cancer, in particular of the colon (Sandler R S., et al., 2003, A randomized trial of aspirin to prevent colorectal adenomas in patients with previous colorectal cancer, New England J. Med., 348:883-890). Otherwise, it is also found that the COX-2 antagonist, such as Celecoxib, Rofecoxib, Nimesulide, meloxicam and Etodolac, can also have anti-cancer activity (Yamazaki R., et al., 2002, Selective cyclooxygenase-2 inhibitors show a differential ability to inhibit proliferation and induce apoptosis of colon adenocarcinoma cells., FEBS Lett., 531(2):278-84). Further, COX-2 is chronically overexpressed in many premalignant, malignant, and metastatic human cancers, and levels of overexpression have been shown to significantly correlate to invasiveness, prognosis, and survival in some cancers (Dannenberg A J., et al., 2003, Targeting cyclooxygenase-2 in human neoplasia: rationale and promise, Cancer Cell, 4(6):431-6). Maximum efficacy is typically dose-limited by COX-1-related toxicities; however, COX-2 inhibitors have been shown to have tumor suppression effect in several animal models of colon, skin, lung, bladder, and breast cancers (Alane T.Koki, et al., 2002, Celecoxib: A Specific COX-2 Inhibitor With Anticancer Properties, Cancer Control, 9(2 Suppl):28-35).
WO94/09811 describes the use of CD44 in treating inflammation or detecting cancer metastasis. The authors show that CD44 is upregulated in inflammatory conditions and CD44 peptides are capable of inhibiting T-cell activation. No data or claims are presented on inhibition of metastasis by CD44 and no claims are made towards use of CD44 for inhibiting tumor growth or angiogenesis. WO 99/45942 discloses the use of HA-binding proteins and peptides, including CD44, to inhibit cancer and angiogenesis-dependent diseases. This patent application uses metastatin, a 38 kDa fragment of the cartilage link protein, as well as a HA-binding peptide derived from this fragment to inhibit pulmonary metastasis of B16 mouse melanoma and Lewis lung carcinoma. In the case of the HA-binding peptide, growth of B16 melanoma on chicken CAM and endothelial cell migration on HA have been inhibited. In both patent applications the use of HA-binding peptides is directly related to their ability to bind hyaluronic acid.
U.S. Pat. No. 8,192,744 shows that soluble recombinant CD44 hyaluronic acid binding domain (CD44HABD) inhibits angiogenesis in vivo in chick and mouse and thereby inhibits human tumor growth of various origins. The invention discloses soluble non glycosylated CD44 recombinant proteins as a novel class of angiogenesis inhibitors based on targeting of vascular cell surface receptor.
Thus, the prior arts, hereinabove cited, disclose the potential use of CD44 and suggest that any effects can be dependent on HA-CD44-interaction. Consequently, all utility ascribed so far to CD44-HA conjugate is directly dependent on their ability to bind hyaluronic acid.
However, some drugs are still not successfully conjugated onto HA and further experiments should be carried out to confirm the potential usefulness of HA as site-delivery carrier of active compound. In particular, the prior art has not shown that the interactions between the surface cell receptor CD44 and a conjugate of HA with an active compound can be profitably exploited for a target delivery of such active compound in diseases characterized by an overexpression of CD44 obtaining an effective therapeutic improvement of the same.
For pathologies, such as for example cancer, in fact, it is still a need felt to have available therapeutic tools balancing an effective cytotoxic effect against the tumoral cells and the cytotoxic effects on the normal cells with a better safety profile.